This invention relates to an optical pickup for recording data on a recording medium, namely, an optical disk and reproducing data from the latter, and more particularly to an objective lens drive device in an optical pickup device in which a movable section with an objective lens is held by wire suspension wires, and to a method of manufacturing the device.
In general, an optical pickup device comprises an optical system which projects a laser beam on an optical disk through an objective lens, and detects a light beam reflected from the optical disk, and an objective lens drive device which moves the objective lens in the focusing direction or the tracking direction of the optical disk.
The aforementioned optical system comprises a light source and a light receiving section. On the other hand, the objective lens drive device comprises a movable section and a stationary section which is fixedly mounted on a mounting base.
The stationary section has a magnetic circuit including a permanent magnet and a yoke. On the other hand, the movable section has an objective lens, a focus coil, and a tracking coil. The movable section is generally supported by some method. A typical example of the movable section supporting method is that the movable section is supported with four suspension wires (hereinafter referred to as "a wire support type", when applicable)(cf. Unexamined Japanese Patent Publication 1-54035 (1989) or 2-232824 (1990).
FIG. 1 shows a typical objective lens drive device of wire support type. In the objective lens drive device, a lens holder (or movable section) 12 having an objective lens 12 is supported by four suspension wires 1 extended from a stationary section 2. The suspension wires are used for supplying current to a focusing coil and a tracking coil. The suspension wires 1 are connected to those coils through holder substrates 5. The suspension wires 1 are fixedly secured to the holder substrates 5 by soldering (at indicated at 6).
In order to accurately perform a data recording and reproducing operation with respect to an optical disk, it is essential that the optical axis of the objective lens is perpendicular to the optical disk. For instance, in the case where, when the movable section (having the objective lens) of the objective lens drive section is moved in the focusing direction, the optical axis of the objective lens is inclined, a comatic aberration occurs, and the signal jitter is increased.
Hence, the objective lens drive device is so mounted on the mounting stand that the optical axis of the objective lens is perpendicular to the surface of the optical disk. Accordingly, in the movable section, the supporting mechanism is so designed that the aforementioned relation is kept unchanged even when the movable section (having the objective lens) of the objective lens drive section is moved in the focusing direction or tracking direction.
In the objective lens drive device of the above-described wire support type, the optical axis of the objective lens is kept perpendicular to the surface of the optical disk even in the case where the movable section is moved in the focusing direction or in the tracking direction if the lengths of the wires supporting the movable section or the wire distances between the ends of them are equal to one another.
However, the lengths of the wires supporting the movable section or the wire distances between the parts of the wires which are near the ends thereof are liable to be fluctuated. The occurrence of fluctuation in wire length or wire distance will be described with reference to FIG. 11.
FIG. 11 shows suspension wires 1 supporting the movable section both ends of each of which are fixed. First ends of the wires 1 are secured to a holder substrate 5 by soldering (as indicated at 6) which is provided for a lens holder, while the remaining second ends of the wires 1 are secured to a base substrate 8 by soldering as indicated at 7.
The first ends of the suspension wires 1 are inserted into guide holes 3a formed in a wire guide section 3 of the lens holder, while the second ends of the wires are inserted into guide holes 2a formed in a wire base 2. In this connection, since members such as the lens holder and the wire base 2 are generally formed with metal molds, it is difficult to form the guide holes 2a which is extremely small in diameter (equivalent to the suspension wires). Even if the diameter d2 of the guide holes can be formed to be the same with the diameter d1 of the suspension wires, the suspension wires, which are fine and tends to be bent, are difficult to smoothly insert into the guide holes. That is, the diameter d2 of the guide holes 2a is about twice as large as the diameter d1 of the wires 1 (for instance d1=80 .mu.m, and d2=150 .mu.m).
Hence, the fixed position of each of the wires 1 is fluctuated as much as the gap between the guide hole 2a and the wire 1. Because of this fluctuation, the lengths of the suspension wires, and the distances L1 and L2 between the parts of the suspension wires 1 which are near the ends thereof are different from one another.
Furthermore, in the objective lens drive device of wire support type, the suspension wires 1 are surrounded by damping material 4 to suppress the low frequency resonance thereof. However, merely by surrounding the wires 1 with the damping material 4, it is impossible to sufficiently suppress the high frequency resonance attributing to pitching and yawing. Hence, in the objective lens drive device disclosed by Unexamined Japanese Patent Publication 7-105551/(1995), as shown in FIG. 12 the wire 1 is bent in the focusing direction, thereby to effectively suppress the high frequency resonance.
As was described above, in the case where the wire 1 is bent in the focusing direction, the high frequency resonance attributing to pitching and yawing can be effectively suppressed. However, the objective lens drive device suffers from the following difficulties:
The wire 1 must be fixedly secured by soldering under the condition that it has been bent to a certain extent. This work is rather troublesome.
In order to electrically connect the suspension wires 1 by fixing both ends of each of the suspension wires 1, it is necessary to arrange printed circuit boards (relaying substrates) at the parts of the wires where the latter are fixed. This fact obstructs the reduction in manufacturing cost of the device. That is, the device is large in the number of components, and high in component cost.
In the case where the suspension wires 1 are fixedly secured by soldering (as indicated at 6), or in the case where the suspension wire 1 is bent in the focusing direction, the distance between the suspension wires 1 on the movable section side is liable to be different from that between the wires 1 on the stationary section side. Hence, the tilt characteristic is low when the lens is moved in the focusing direction. In the case where the wire distance between the first ends of the wires is not equal to that between the remaining second ends of the wires, the optical axis of the objective lens is not perpendicular to the surface of the optical disk. Furthermore, the objective lens drive device suffers from the comatic aberration and the increase in jitter of the signal when the tilt characteristic is lowered.